雪崩実績図を用いた雪崩の発生条件分級加点図の評価とその改良

抄録

Japanese mountain areas have abundant snowfall in the Sea of Japan side, and avalanches tend to cut off the traffic and crush houses. Thus, many avalanche disasters brought heavy damages. Therefore, it is important to improve avalanche risk estimation method and to map the risk. Avalanches are likely to occur at slope where snow depth is deep, slope inclination is steep, vegetation is sparse, and there are shallow furrows on bedrock incised by past frequent avalanches. Previous study scored these four explanatory variables, and mapped the risk based on the accumulated scores. However, it is difficult to estimate adequate weights on the four variables in accumulating them. This is because the relation between actual avalanche and the four variables is seldom to be revealed simultaneously.
This study aims to investigate the relation between them and propose an improved avalanche risk map. Study area was selected in Yamakoshi district in Nagaoka city where some 2, 000 avalanches, whose distribution was mapped, occurred under the influence of the recorded snowfall in 2004-2005 winter. In the investigation and the mapping, five-meter-grid data derived from aerial photo interpretation and image processing, and airborne LIDAR data were used.
At each grid, ideally, the higher the accumulated score is, the higher the avalanche risk. Comparing with the previous study's risk map, this study could present a better risk map where the accumulated score showed very high positive correlation with avalanche ratio.